Some achilles heel, huh. 
This has always been a tricky little scripture for some who say Israel was deported in 721 B.C. to Assyria....and never came back. This scripture has also been used by many to "Absolutely Prove" those of us holding that position....of our error. The Tribe of Asher, of course....being one of the ten northern tribes was never mentioned in Old testament scripture, along with the other nine.....of ever returning to the Promised Land.....Israel.
Judah (Judah, Benjamin & Levi) was exiled herself to Babylon 125 years later....but the scriptures record their return thoroughly. The Books of Ezra and Nehemiah tell of the return of Judah from the Babylonian captivity after 70 years and mention nothing about the other tribes at all! Only Judah, Benjamin and Levi are spoken of in these books.
So......where did Anna of the tribe of Asher come from? If you notice.....she is a pretty important lady! Luke calls her a Prophetess....the daughter of Phanuel of the tribe of Asher. For her to have rated all these distinctive adjectives she evidently was being singled out. Indeed, she along with Simeon, become the first prophets of the New Testament. They both identify Our Lord as the promised Messiah immediately. [Luke 2:25-38] Luke also mentions other female prophets, Philip's daughters....[Acts 21:9] but does not specifically say of what they prophecy.
From reading the scripture it appears that Anna never leaves the temple and the question....I assume....is, "What is she doing here (in Jerusalem) if she and her tribe have been exiled?"
We in the Twenty First Century consider the ten northern tribes lost to history. We don't know for sure who they might be.....(we have opinions), but there remains no definitive, authoritative source we can turn to for the exact location of the descendants. On the other hand....the folks of the First Century (this includes Luke and the others) knew exactly who they were....and where they were!
[Matthew 10:5-6] These twelve Jesus sent forth, and commanded them, saying, Go not into the way of the Gentiles, and into any city of the Samaritans enter ye not: But go rather to the lost sheep of the house of Israel. When Our Lord gave this commandment to the Twelve He did not pass out any Rand McNallys to them. They all knew where Israel was!
[John 21:15-17] So when they had dined, Jesus saith to Simon Peter, Simon, son of Jonas, lovest thou me more than these? He saith unto him, Yea, Lord; thou knowest that I love thee. He saith unto him, Feed my lambs. He saith to him again the second time, Simon, son of Jonas, lovest thou me? He saith unto him, Yea, Lord; thou knowest that I love thee. He saith unto him, Feed my sheep. He saith unto him the third time, Simon, son of Jonas, lovest thou me? Peter was grieved because he said unto him the third time, Lovest thou me? And he said unto him, Lord, thou knowest all things; thou knowest that I love thee. Jesus saith unto him, Feed my sheep.
So......where do we find Peter...eventually? We don't ever find him in Rome, but we find him in Babylon writing to the folks on the southern shores of the Black Sea. [1 Peter 1:1-2] Peter, an apostle of Jesus Christ, to the strangers scattered throughout Pontus, Galatia, Cappadocia, Asia, and Bithynia, Elect according to the foreknowledge of God the Father, through sanctification of the Spirit, unto obedience and sprinkling of the blood of Jesus Christ: Grace unto you, and peace, be multiplied.
The words "Strangers Scattered" in the Greek means "Israelites of the Dispersion" living in foreign countries. That's who these folks in [1 Peter 1:1-2] were and that's where a portion of them lived.....500 miles from Jerusalem. Other tribes lived in Babylon....closer yet and portions of their populations still visited for the festivals....those who had not forgotten. Obviously Anna would be counted in this number (folks who had not forgotten).
I always like pointing out the fact that Josephus was well aware of the location of Israel in the first century and he writes of that in Antiquities XI, Chapter 5, Paragraph 2, lines 6-7. He says: "There are but two tribes in Asia and Europe subject to the Romans, while the ten tribes are beyond Euphrates till now, and are an immense multitude, and not to be estimated by numbers." The two tribes he mentions are Judah and Benjamin (The Jews) that are subject to the Romans. The Levites owned no property so were counted among the others. The ten tribes are known to him as "Israel" and they are beyond the Euphrates (Babylon/Persia).
The point I'm making here is that everyone knew where most of Israel was in the First Century and many of the tribes were still in what we would call the Mid east. Other tribes and parts of other tribes may have already migrated through the Caucasus Mountains and started to spread out through Asia and Europe......but many of them remained fairly close to Jerusalem and those that remembered their heritage....... visited.
Anna's Father was Phanuel and it was said he descended from Asher.....or did it? [Luke 2:36] "Young's Literal Translation" And there was Anna, a prophetess, daughter of Phanuel, of the tribe of Asher, she was much advanced in days, having lived with an husband seven years from her virginity. Was Anna of the tribe of Asher or was Phanuel of the tribe of Asher or were they both of the tribe of Asher. Anna could have married an Asherite (her husband of seven years) and the statement "A daughter of Phanuel" could also mean she was descended from Phanuel.
[1 Chronicles 4:4] And Penuel the father of Gedor, and Ezer the father of Hushah. These are the sons of Hur, the firstborn of Ephratah, the father of Bethlehem. Verse 1 shows this Phanuel (Greek spelling versus Hebrew) as a descendant of Judah! Was Anna just a descendant of this man and had she married into the tribe of Asher. Who knows! It's not important!
The fact that the Northern Tribes were exiled and never returned as a body is scripture and all the nitpicking about this verse [Luke 2:36] is silly. It shows one person out of millions of Israelites, mentioned as being in and around Jerusalem awaiting the Messiah. There is absolutely no reason to question the veracity of the continued exile of the Ten Tribes because of Anna. She....as a daughter of Israel.....had more right than the Romans to be there.
Some achilles heel, huh.